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in creator/contributor: "Follstaedt, D.M."

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Reciprocal-Space Analysis of Compositional Modulation in Short-Period Superlattices Using Position-Sensitive X-Ray Detection

Epitaxial growth of AlAs-InAs short-period superlattices on (001) InP can lead to heterostructures exhibiting strong, quasi-periodic, lateral modulation of the alloy composition; transverse satellites arise in reciprocal space as a signature of the compositional modulation. Using an x-ray diffractometer equipped with a position-sensitive x-ray detector, we demonstrate reciprocal-space mapping of these satellites as an efficient, nondestructive means for detecting and characterizing the occurren… more

Date: November 10, 1998

Creator: Ahrenkiel, S. P.; Follstaedt, D. M.; Lee, S. R.; Millunchick, J. M.; Norman, A. G.; Reno, J. L. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Performance of Ultra Hard Carbon Wear Coatings on Microgears Fabricated by Liga

Stiction and friction are of concern for the reliable, long-term application of Ni-alloy micromachines. We have found that the application of a 30-70 nm hard carbon coating produces a significant reduction in the friction coefficient and wear rate of electroformed Ni substrates in reciprocating sliding contact under simulated MEMS operating conditions. To evaluate the performance of coated components, a series of 70-pm-thick microgears ranging in diameter from 0.2 to 2.2 mm were fabricated from… more

Date: December 18, 1998

Creator: Ager, J. W., III; Brown, I. G.; Christenson, T. R.; Dugger, M. T.; Follstaedt, D. M.; Knapp, J. A. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Considerations relating to pulsed-beam modification of materials

Ion implantation has been shown to produce unique improvements in the properties of a wide range of materials. This technology has been extensively used for doping of semiconductors, where the required doses and implantation depths are relatively modest and readily achieved with commercial implanters. Other applications of ion implantation currently being pursued at a commercial level include the synthesis of buried second-phase layers in Si and the improvement of metal surface properties such … more

Date: January 1, 1990

Creator: Myers, S. M.; Follstaedt, D. M.; Bourcier, R. J.; Dugger, M. T.; McIntyre, D. C. & Rader, D. J.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Understanding and control of optical performance from ceramic materials

This report summarizes a two-year Laboratory-Directed Research and Development (LDRD) program to gain understanding and control of the important parameters which govern the optical performance of rare-earth (RE) doped ceramics. This LDRD developed the capability to determine stable atomic arrangements in RE doped alumina using local density functional theory, and to model the luminescence from RE-doped alumina using molecular dynamic simulations combined with crystal-field calculations. Local s… more

Date: June 1, 1998

Creator: Barbour, J. C.; Knapp, J. A.; Potter, B. G.; Jennison, D. R.; Verdozzi, C. A.; Follstaedt, D. M. et al.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Observation of excitonic and band-to-band behavior in ordered InGaP{sub 2} alloys

Photoluminescence measurements on ordered InGaP{sub 2} were studied as a function of temperature, laser power density, and magnetic field. The temperature varied between 1.4 and 300 K, the laser power densities ranged from 10 nW/cm{sup 2} to 20 W/cm{sup 2}, and the maximum magnetic field was 13.6 T. The data show both excitonic and band-to-band behavior, depending upon the incident laser power density. A consistent interpretation of all data leads to a type-II valence-band offset between the or… more

Date: September 1, 1994

Creator: Jones, E. D.; Follstaedt, D. M.; Lee, H.; Nelson, J. S.; Schneider, R. P. Jr.; Alonso, R. G. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Spontaneous lateral composition modulation in InAlAs and InGaAs short-period superlattices

The microstructure of spontaneous lateral composition modulation along the [110] direction has been studied in (InAs){sub n}/(AlAs){sub m} short-period superlattices grown by molecular beam epitaxy on (001) InP. X-ray diffraction and transmission electron microscopy show that global strain ({var_epsilon}) in the superlattice reduces the degree of composition modulation, which disappears for the absolute value of {var_epsilon} > 0.7%. For tensile strains of {var_epsilon} {approx} +0.4%, they fin… more

Date: July 11, 1997

Creator: Follstaedt, D. M.; Twesten, R. D.; Millunchick, J. M.; Lee, S. R.; Jones, E. D.; Ahrenkiel, S. P. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Microstructure of compositionally modulated InAlAs

The authors have observed spontaneous, lateral composition modulation in tensile InAlAs alloy films grown as short-period superlattices on InP (001). They have analyzed these films using transmission electron microscopy, x-ray reciprocal space mapping, and polarized photoluminescence spectroscopy. They find the growth front is nonplanar, exhibiting {approximately} 2 nm deep cusps aligned with the In-rich regions of the compositionally modulated films. In addition to the measured 15 nm wavelengt… more

Date: December 31, 1996

Creator: Twesten, R. D.; Millunchick, J. M.; Lee, S. R.; Follstaedt, D. M.; Jones, E. D.; Ahrenkiel, S. P. et al.

Item Type: Report

Partner: UNT Libraries Government Documents Department

open access

Characterizing Composition Modulations in InAs/AIAs Short-Period Superlattices

The formation of quantum wires has much interest due to their novel electronic properties which may lead to enhanced optoelectronic device performance and greater photovoltaic efficiencies. One method of forming these structures is through spontaneous lateral modulation found during the epitaxial growth of III/V alloys. In this paper, we report and summarize our investigations on the formation of lateral moduation in the MBE grown InAlAs/InP(001) system. This system was grown as a short-period … more

Date: April 26, 1999

Creator: Ahrenkiel, S. P.; Follstaedt, D. M.; Jones, E. D.; Lee, S. R.; Mascarenhas, A.; Mirecki-Millunchick, J. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Photoluminescence Studies of Lateral Composition Modulated Short-Period AlAs/InAs Superlattices

We present low temperature photoluminescence data for a series of spontaneous lateral composition modulation in (AlAs){sub m}/(InAs){sub n} short period superlattices on InP with differing average lattice constants, i.e., varying global strain. The low temperature photoluminescence peak energies were found to be much lower than the corresponding energy expected for the equivalent In{sub x}Al{sub 1{minus}x}As alloy. The bandgap energy reductions are found to approach 500 meV and this reduction i… more

Date: January 4, 1999

Creator: Ahrenkiel, S. P.; Follstaedt, D. M.; Jones, E. D.; Lee, S. R.; Mascarenhas, A.; Mirecki-Millunchick, J. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Energetic Particle Synthesis of Metastable Layers for Superior Mechanical Properties

Energetic particle methods have been used to synthesize two metastable layers with superior mechanical properties: amorphous Ni implanted with overlapping Ti and C, and amorphous diamond-like carbon (DLC) formed by vacuum-arc deposition or pulsed laser deposition. Elastic modulus, yield stress and hardness were reliably determined for both materials by fitting finite-element simulations to the observed layer/substrate responses during nanoindentation. Both materials show exceptional properties,… more

Date: January 1, 1998

Creator: Follstaedt, D. M.; Knapp, J. A.; Myers, S. M.; Dugger, M. T.; Friedmann, T. A.; Sullivan, J. P. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

The nature and origin of lateral composition modulations in short-period strained-layer superlattices

The nature and origin of lateral composition modulations in (AlAs){sub m}(InAs){sub n} short-period strained-layer superlattices (SPS) grown by molecular-beam epitaxy on InP substrates have been investigated by X-ray diffraction, atomic force microscopy, and transmission electron microscopy. Strong modulations were observed for growth temperatures between approximately 540 and 560 C. The maximum strength of modulations was found for SPS samples with InAs mole fraction x (= n/(n+m)) close to app… more

Date: February 28, 2000

Creator: Norman, A. G.; Ahrenkiel, S. P.; Moutinho, H. R.; Ballif, C.; Al-Jassim, M. M.; Mascarenhas, A. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

open access

Ultrahard Multilayer Coatings

We have developed a new multilayer a-tC material that is thick stress-free, adherent, low friction, and with hardness and stiffness near that of diamond. The new a-tC material is deposited by J pulsed-laser deposition (PLD) at room temperature, and fully stress-relieved by a short thermal anneal at 600°C. A thick multilayer is built up by repeated deposition and annealing steps. We measured 88 GPa hardness, 1100 GPa Young's modulus, and 0.1 friction coefficient (under high load). Significan… more

Date: May 1, 1999

Creator: Chrzan, D.C.; Dugger, M.; Follstaedt, D.M.; Friedman, Lawrence H.; Friedmann, T.A.; Knapp, J.A. et al.

Item Type: Report

Partner: UNT Libraries Government Documents Department